I have triple checked my timing and timing belt. Everything is dead on. As soon as engine startes to warm up it starts, 1,500 rpm then 700 rpm and alternates like this about every 3 or 4 seconds. Runs good otherwise. Have reset ECU no changes. I am at wits end. This started 1 week after I got my ZC on the road. I'm certain this has been discussed before. The CHiltons manual has nothing about this symptom. Have found NO vacume leaks. Although I could have missed a minor one. But doubt that is it. Any Ideas from those more experienced with this than I am. Thanks for any advice/help.

 

Which ecu are you using???

 

I have the ZC ecu. Got it from the importer where I got the engine. 112 limiter didn't matter to me. Passing emissions and running smooth did. Well that part was true the first week but not now.

 

My neighbor was using an 89 integra ecu and it did that for awhile after he got his swap. Have you checked the ignition timing and the distributor. 88-91 civic/crx vehicles are known for having notoriously bad distributors. Just a thought

 

most likely the cold intake butterfly valve in your throttle body is gummed up, this happened to my integra too and the engine check lite never came on, take the throotle body off and on the inside on the left as you look into the opening is the cold intake valve, it can be cleaned with petrol, i just blocked mine with a piece of jaycloth, as i couldnt be bothered at the time taking the whole thing off, that was over a year ago and i've never had bother since. this valve provides extra air on cold mornings, the valve is supposed to close when the engine reachs sufficient temp and the ECu sends the signal to close the valve as its all gummed up with crap taken in through the intake it is unable to close properly, as the ECu has sent the signal to close it, the engine drops the revs as the valve should now be closed, but as its open the engine is getting too much air, the ecu then tries to close the valve again when it detects the extra air and so on, this causes the erratic idle, fairly simple job to take T/b off and clean it

 

Seems like everyone is haveing this problem...including me. Someone said to check the IAC...Idle air control sensor....its on the throttle body, has three wires going to it. they said to turn a screw in there to adjust it.(b16) I never found a screw...I found what I thought was the IAC and tryed to adjusted it, but didn't seem to do much. Do a seach...it was just talked bout last week sometime...possibly in the CRX forum

ALso, I pulled the throttle body off, it was black in there...like tons of black oil(seemed like it was turning back to coal in there) ...I could see some stuff being in there...but not that much. I could dip my finger in there...and smer a line bout 6 inchs on my other hand. Should it be that dirty? should I wash it out with degreeser, and after its been cleaned is should I do anything to protect it(the inside of the intake manifold)?

 

Thanks for the advice. I'll try that tonight. The thing that made it different than some of the other idle problems described is that It idled smooth untill the engine started to warm up. On Bitter cold mornings it takes quite a while longer to start than warm afternoons. Like your description the idle drop off is abrupt, like slowly reving the motor then adbruptly slipping your foot off the gas. The car runns smooth as silk otherwise. Due to the impecable cleanliness inside the motor and the the condition of the cylinders from the pan side this really has to be a low milage motor. My other car is impecably maintained and it is nowhere near as clean inside. I am replacing the new timing belt on this motor with an OEM one. Dang GATES belts are garbage. THis thing jumped time 3 times the first week. THough that is not the current cause of the idle problem. I will be checking and cleaning tonight. Also the dashpot for the idle is not causing this, It is doing the surging with the main throttle closed and not moving. The idle speed shoots up if I pull off the vacume line to it and plug the vacume line. I hope your suggestion clears up the problem. It is aggrivating me to no end. Thanks.

 

I had the same problem. I can't figure out what it was. It was really bad for a while. I replaced the AICV and it didn't help at all. I switched from my teg ECU back to my Si, and it stopped. I hate driving a ZC with the crappy Si ECU, so I switched back, and it was fine for a while, then it started again. I switched back the Si, and it kept doing it. I switched every sensor, relay etc that I could think of out of my parts car, and it only did it one time since then. It only did it when warmed up. It was the exact symptoms you're talking about. Let us know what you all find out. I'm afraid mine will start once it gets warm outside again.

 

I asked the same question about a month ago, nobody really new what it was someone told me it could be a bad relay. Then suddenly it stopped doing it for about 1 month and just this saturday morning it started doing it again. But ive noticed that it has something to do with the temperture outside, confused???? Im going to ask my local mechanic and see if I can get a response. I'll post when I find out.

 

I pulled the Throttle body off and cleaned it , it was fairly cursty, Also pulled off the EACV valve and cleaned that, The screan had a lot of crud on it, also took time to clean out the vacume ports, took out the Idle air blead screw and cleaned it of crud. However I managed to lean on the air intake bolted to the damned radiator and cracked the **#$%@! radiator tank. So now I have the pleasure of buying a new radiator. BUt for the while I ran it it seemed to run better, I did notice the idle bleed screw was bleeding a bit too much air and turned that down to idle about 700 which is a fair amount lower than it was idling scince I put it in. I'll let you guys know if that was the cause after I have a new radiator and have it trunning long enough to see if it starts again. My symptoms were the idle was increasing to 1,500 then abruptly dropping to 700 like somebody was reving the motor. but the throttle was not moving at all from the dash pot if you looked under the hood. if you pushed the gas just enough to get you to about 1,600 it stopped all together from the reving and stayed stable. I may have this one licked but its too soon to be sure.

Oh, I want to add mine started doing this 1 week after swap. and has been VERY cosistant once engine has warmed up enough to register on the temp gauge. Which on a cold morning takes longer than a warm day. Not at all intermittant, been doing this for a solid week.


[Modified by virginia_dude, 6:25 PM 3/5/2002]

 

I promised you guys a follow-up when I had the new radiator in it so here it is. This car runs better than it ever has( not that its that long). It was running good and smooth before the surging started but was disappointed in the power, I had been expecting a huge increase over the 92hp D-15 but had a marginal increase at the bottom end and a nice amout higher up.. Now its a huge jump in torque off idle and goes up from there. Smooth idle NO surging anymore. This is not going to be a blanket answer to all of the idle problems but I'm sure SOME of you may have simular problems. Here are my recomendations.

1: CHeck or replace your PCV valve. it should rattle when you roll it end over end. better yet if you don't remember when it was replaced , just put a new one on. It can cause a vacume leak into your engine, and you'll see a jump in oil consumption or it will cause a pressure increase in your engine and cause oil to leak past your seals and gaskets depending on its position where it sticks.

2. Clean the throttle body. Mine was sticking ever so slightly but I pulled it off to check and clean passages more easily. I had a lot of black greasy crud on the inside that I cleaned , also on the bottom of the intake runners. I cleaned it with a brush a rag and Throtle body cleaner. pay close attention to the small vacume ports.

3: Check to see just where your Idle air bleed screw is adjusted. I had a loud rushing sound when it was idling before with the air intake off. the big brass screw at the top side corner of the thottle body of the ZC looking from the passenger side of the car it where its at. I had a lot of crud on it and the seat of the valve body. I noticed it seemed to be way out. seated it and backed it out a turn and a half which was a good starting point, adjusted it for a good idle speed of about 750rpm. No more loud rushing sound. Screw was a lot further out than that before.

4. Took off the EACV valve assy. THe screen had a lot of black greasy crud on it, cleaned the whole assy well with throttle body cleaner.

Reassembled items using a thin film of HondaBond as I didn't have new gaskets on O-rings.

Fired up the car and What a HUGE difference. Car ran smooth before the surging started. But it never had the kind of torque and power it has now. My situation I believe was caused by several things and not one single thing. The computer was compensating until things got too much for it to handle and thats when the surging started. Its no guarantee of a fix but if you check these items maybe you'll get lucky.


[Modified by virginia_dude, 9:31 AM 3/8/2002]

 

I can't believe nobody mentioned anything about coolant level or if the system was properly bled. Having air bubbles in your coolant is the number 1 cause for idle surge! The temp of the coolant is what brings the idle down from 1500 to idle. If there are air bubbles they read to the temp sensor as cold coolant. Yikes.

Damn! I bet after you replaced your radiator the surge went away because the cooling system was properly filled.

 

That could be true for some people with this problem. But I did make double certain my coolant system was properly purged. My need for a new radiator was not due to a leak that developed and caused coolant loss but due to leaning on the air intake tube that was bolted to the radiator causing a 3" crak in the upper tank while performing the other work I was doing. Car was not driven from the point of cracking the radiator to replacement of the radiator. So in this specific situation that wasn't causing my problem. But you have a very valid point that I failed to mention.

 

Some people also complain that after a valve adjustment the idle surges. This what happend to me. I adjusted my valve because they were tapping, when i was done and put everything back together i started it up. At first everything was cool no more tapping. The after it warmed up at idle it surges and almost sound's like it's missing. I'm going to readjust the intake side and see if that helps. I'm going to put it at .006 and exhaust at .008. I'm hoping this will solve the problem cause it never did it before the adjustment.

 

http://www.zdyne.com

the ZC engine has problems with any ECU that is not it's intended JDM ZC ECU. Zdyne has a ECU program that they load directly into your existing ECU (whatever youre using), that fixes the erratic idle, fixes the running rich at idle, fixes everything. Check out their site, they can help ya.

 

In My case I got a JDM ZC ECU from the importer I bought my engine from, so I have had zero experience with a non ZC ecu. My problems appeared to have caused an excessively lean idle. At least 2 of them positively did. Guess that goes to show there are quite a few possibilities with this problem.

 

In addition, I ran an integra ECU for about 2 years with no problems at all before my idle problem started. It had the idle problems for about 1 month and its been fine ever since. This is year number 3 or 4 with that ECU and motor combo, and there have been no problems other than the surging idle.

Someone on here posted that they had bought the Zdyne ZC ECU and it ran so poorly that they put the teg ECU back in. I can't remember now who it was though.

 

i dont know if this might help, but i rember doing a swap for one of my friends it wasnt a ZC but it was a si, it had the same symptons as you were describing, and guess what we went through; timing, idleing, wirings, and ecu codes, just found out that behind the intake manifold there are 2 plugs with i think 2 to 3 wirings that look just like each other. and if those two are plug in differently those symptons will occur. so i would start checking those plugs first.